The present invention is directed to commissioning methods for subsea pipelines. More specifically, the present invention is directed to a commissioning method wherein the operation is carried out on the seabed rather than at the surface.
U.S. Pat. No. 5,883,303 discloses and describes an apparatus and method for pigging, flooding and pressure testing pipelines.
The above patent is directed to the testing required when a new pipeline is placed in operation. However, when commissioning a subsea pipeline, or adding a new segment to an existing offshore pipeline, it is often desired to follow the hydrostatic pressure testing with an inert gas or specified medium to purge/dewater the subsea pipeline, and/or inject specified chemicals, to dry the inside of the line before flow of the oil/gas in the pipeline.
The dewatering of a subsea pipeline by the prior art has been at surface level, usually on a surface vessel, boat, structure or platform. This requires that long lines of coiled tubing, hose, or pipe, be used. The prior art method uses large distances of coiled tubing, hose, or pipe, to connect the pipeline to a pump mobilized on the deck of a support vessel to remove the water and dry the line before product is allowed to pass through the line. Also required by the prior art method are large pumps, compressors, compressor boosters and surface support vessel and/or vessels, to support the large volume of compressed gases and fluids pumped through the significant distances to fill the new portion of the pipeline with the gas and fluids.
The method of the present invention eliminates the larger volume of compressed gas and fluids, the higher pressure of the compressed gas and fluids, the large pumps/compressors, compressor boosters, long distances of coiled tubing/hose/pipe, and substantial surface support vessel/vessels, all required by the prior art methods.
The present invention is directed to a method for completing the commissioning of a subsea pipeline by purging with a compressed gas to dewater and dry the line wherein the operation is done on the seabed. More specifically, the method is carried out with a subsea vechicle (hereinafter xe2x80x9cSVxe2x80x9d) that powers pumps located on the seabed or that are carried by the SV to inject/remove chemical, dewater, and dry, the pipeline. The present invention may be part of the commissioning of a new or old pipeline or a new portion of a pipeline in which a purging of the line with a compressed gas and drying of the line is required. After commissioning, product flows through the pipeline.